In our last SwedeTech’s Corner, we started the troubleshooting guide for clutch kart engines, addressing no sign of spark and engines that may be starving for fuel. In this edition we will continue the guide. Next month’s SwedeTech Corner will go into troubleshooting Shifter Engines. So enough rambling, let’s continue.
Before trying to restart the engine, always inspect the inside of the engine utilizing an inspection light. This can be done by removing the spark plug and looking inside the cylinder with the inspection light. Look for any damage on the piston or cylinder walls. If you see damage, do not run and consult your engine builder. You will see this statement many times in this troubleshooting guide. This should always be the first step in any engine troubleshooting. I’ve seen countless engines that had a huge parts failure or a seized top end, and the mechanic just kept cranking the engine over without looking inside to see if the engine was even functional.
Engine Performs as if it is Flooded
- Before trying to restart the engine, always inspect the inside of the engine utilizing an inspection light. This can be done by removing the spark plug and looking inside the cylinder with the inspection light. Look for any damage on the piston or cylinder walls. If you see damage, do not run and consult your engine builder.
- Double check your baseline carburetor settings. If you are using a pumper style carb with tunable needles, remove the needles and look for damaged needle tips. Before removing the needle, mark each needle’s position and keep track of how many turns out each needle is by turning the needle all the way in until it closes while counting the turns. When you replace the needle, turn it all the way in until it stops and then open it back up to its former position.
- Make sure the fuel tank has proper venting to the atmosphere. If you are using a catch tank on the vent line, make sure the catch tank is properly vented. On most karting applications, supply, return, and venting fuel line connections with an I.D. of 3/16″ (4.8mm) should be adequate for proper fuel supply and venting. Always inspect all fuel line connections, especially on the inside of the plastic tank connections. Any obstruction inside the fuel line or connections will cause fuel supply issues.
- Always run a fuel filter inline before the carburetor and/or fuel pumps. If you think a fuel filter is causing a restriction, find a better one that will not cause a fuel restriction. Carburetors do not perform properly when they are filled with debris.
- Check the fuel inlet needle and seat for damage or debris. This can be done visually by removing the needle. If you feel the needle and seat are fine, check the pop off. When in doubt, rebuild it with the proper parts.
- Remove the carburetor and intake manifold and inspect the reeds for damage. Cracks, frays, and missing pieces will affect how the engine performs. Inspect the reed cage and the rubber coating for any damage or debris. If it is questionable, replace.
- Inspect the exhaust system for clogged exhaust cores or excessive carbon build up. If the end caps are removable, remove them and inspect the inside of the pipe. Before cleaning any exhaust component, reference your rules for modifications. Some rules do not allow any machining or porting on certain parts. We’ve seen a number of parts that were expensive paper weights because the previous user got carried away with a clean up tool or sanding roll.
- If you are using an air filter, do not oil the filter before a tuning session or track session. Adding oil to many filters will restrict the air flow, causing the engine to run rich. When possible, try to use a stiff filter that will not collapse under the suction of the engine’s intake stroke.
- Check the exhaust system for a forgotten or lost shop rag, usually blue or red in color. The tell tale sign of a rag in the exhaust, engine runs on the stand and sometimes idles fine. Once you are applying a load to the engine, it hesitates and stutters. It sits for a second and you can fire it right up, only to repeat the process. Don’t tell your friends when you find the problem, only tell them it was a bad spark plug.
- Check for any loose or bad electrical connections. Sometimes when the ignition system starts to fail, the engine can start to run rich. It can also start burning holes in the middle of the piston.
- Double check your fuel and if you are questioning the oil mixture or quality, replace the fuel and oil and remix.
Engine Lacks Acceleration and Top End Power
- Before trying to restart the engine, always inspect the inside of the engine utilizing an inspection light. This can be done by removing the spark plug and looking inside the cylinder with the inspection light. Look for any damage on the piston or cylinder walls. If you see damage, do not run and consult your engine builder.
- Double check all electrical connections. Refer to the electrical spark section outlined above. Electrical problems can hinder engines performance under a load without completely failing.
- Check your carburetor settings and compare to your baseline notes. Typically, if the engine will run to the higher rpm range, but feels lazy and lacking torque, the tuning can be lean on the full throttle position. If the engine labors and will not achieve high rpm’s, this can be a sign of a rich condition.
- Check your chain tension and condition of the chain. If the chain is tight, it will hinder acceleration and performance. If the chain is discolored from heat or has tight spots, replace. At the same time, inspect engine sprocket and axle sprocket.
- Remove chain and water pump pulley belts and spin the rear axle. If there is noticeable drag, inspect the brake rotor, brake pads, axle bearings, and axle bearing cassettes. Your engine is a work horse, the greater the load or resistance, the harder it is for the engine to achieve maximum performance.
- Inspect the exhaust side of the piston skirt. Do you see excessive “blow by” under the ring land. If the piston skirts look heavily worn or you see excessive exhaust discoloration below the ring, it may be time for top end service.
This guide was created to help you, but it is only a guide. There are many factors that we did not include that can also contribute to poor engine performance. When diagnosing a problem, you need to look at all factors. If the engine performs poorly in only one section of the track, try to think about other influences, not just the engine. You will also want to consider the following while troubleshooting:
- How is your chassis handling? (For more on how this relates to engine performance, refer to the Stable or Free – Which is Faster? article elsewhere in this issue)
- How is your driving affecting the chassis and engine?
- What did you recently change that may have caused a problem? (For instance, many times putting new tires on will over-stick the kart and actually hinder acceleration as opposed to improving it. See Tuning with Tires – FKI December 2010)
- When was the last time you performed a thorough inspection of all chassis and engine parts?
- Are other participants having the same problems?